Treating hydrocarbon fluids



Oct. 7, 1941. P C. KEN-H, JR, ETAL 2,258,016

TREATING HY'DROCARBON FLUIDs Fi1ed Aug. 12, 1939 2 sheets-sheet 1 Oct. 7, 1941. P. c. KEITH, JR., ET Al.

TREATING HYDR'OCARBON FLUIDS Filed Aug. l2, 1959 2 Sheets-Sheet 2 mkh..

Patented Oct. 7, 1941 TREATIN G HYDROCARBON FLUIDS Percival C. Keith, Jr., Peapack, and Luther R.

Hill, Rad

burn, N.'J., asslgnors to The Poly- ,merization Process Corporation, Jersey City,

N. J., a corporation of New Jersey Application ugust 12, 1939, Serial No. 289,862

(Cl. s2-175.5)

3 Claims.

'Ihis invention relates to a process for the conversion of lower molecular weight hydrocarbons into hydrocarbons of higher molecular weight and is directed particularly to the conversion of normally gaseous hydrocarbons into normally liquid products suitable for use as motor fuel.

It is an object of the invention to provide a process for the polymerization of normally gaseous hydrocarbons at elevated temperatures and pressures into normally liquid products including an improved method for separating from a mixture of hydrocarbons substantially all of the normally gaseous hydrocarbons which it is desired to subject to the polymerization operation of the process.

Another object of the invention is a process for the conversion of normally gaseous hydrocarbons into normally liquid products which is especially adapted to function efficiently on hydrocarbon charging stocks varying greatly in composition.

A still further object of theinvention is a process for the conversion of normally gaseous hydrocarbons into normally liquid products providing for an improved method of cooling the hot reaction products giving rise to an improved distribution of the total heat content of the h ot reaction products within the system and .an improved fuel economy.

In accordance with my invention a hydrocarbon mixture comprising normally gaseous hydrocarbons from any suitable source, as obtained for example in the cracking of hydrocarbon fluids or other refinery operations processing hydrocarbon fluids, is charged to a primary'stripping zone wherein a lighter normally gaseous hydrocarbon fraction, comprising substantially alll constituents lighter than those desired as charge to the conversion operation, for example, hydrogen,l

methane, ethylene and ethane, is separated from a heavier hydrocarbon fraction comprising normally gaseous hydrocarbons desired as 'charge to the conversion operation. This heavier hydrocarbon fraction is pumped from the primary stripping zone to a conversion zone wherein it'is subjected to polymerizing conditions oi' temperature and pressure, for example, to temperatures of from 750 F. to 1250 F., or if suitable catalysts are employed at a lower temperature, and under a pressure in excess of about 400 pounds per sq. in. Conditions within the conversion zone are selected to produce an optimum rate of conversion of normally gaseous hydrocarbons into normally liquid products boiling within the motor fuel boiling range.

Reaction products emanating from the converthe primary stripping zone wherein it is separated, together with the fresh charge, into a lighter normally gaseous hydrocarbon fraction yand a heavier normally gaseous hydrocarbon fraction comprising normally gaseous hydrocarbons suitable for recycling to the lconversion zone. y

The lighter normally gaseous hydrocarbon fraction separated in the primary stripping zone, even though suchy zone functions at optimum conditions of eiiiciency of a commercial operation, will contain constituents as. for example, propane and propylene, which are desirable as charge to the conversion zone. To effectthe conservation and utilization of these desirable constituents of the lighter hydrocarbon fraction, the primary stripping zone is operated in intimate conjunction with a recovery system to which the lighter normally gaseousl hydrocarbon fraction leaving the stripping zone is passed.

The recovery system comprises two cooling zones within which desirable constituents of the lighter hydrocarbon fraction emanating from the primary stripping zone are condensed and returned to the primary stripping zone. Such desirable constituents returned to the primary stripping zone function as reflux for the fractionating section of the primary stripping zone and the intimate operation of the primary stripping zone with the recovery system is an important feature of the invention which is made more fully apparent by the subsequent description thereof.

In its preferred embodiment the cooling zones -of the recovery system consist of two indirect heat exchangers wherein the lighter hydrocarbon fraction emanating from the primary stripping zone is subjected to indirect heat exchange with a liquefied normally gaseous hydrocarbon entering the cooling side of the exchangers at, or slightly below, its boiling point. In its function as a cooling medium the liquefied normally gaseous refrigerant is vaporized in the indirect heat exchangers.' drawing its latent heat of vaporization from the lighter normally gaseous hydrocarbon stream being cooled. The desired temperature of the cooling zones is maintained by controlling the pressure upon. and therefore the boiling point of, the liquefied normally gaseous hydro- In the preferred embodiment oi the recovery system oi the process of the invention the use of two independent cooling zones permits operation of the :d rst cooling zone at a higher temperature thereby necessitating the condensation of only a minimum quantity of material in the second and cooler zone wherein the refrigerant is maintained at a lower pressure and consequently requires greater eiort and expense of recompression and cooling.

A feature oi theinventlon is the adaptability ci the process to a wide variety of charging stocks. Ii, for example, a charge is used which comprises constituents heavier than those desired as charge to the conversion'zone, the charge may be passed into an accumulating zone whence it is passed directly into the hot reaction products leaving the conversion zone. Ii desired a fra-ction of the charge comprising substantially all oi those constituents heavier than those desired' for the conversion operation is passed into the is contacted with a scrubbing medium to absorb constituents heavier than the undesired lighter constituents of the charge in the absorbing medium. The resulting rich absorbing medium comprising the absorbed desirable constituents of the charge is stripped of the desirable constituents of the charge and the desired constituents of the charge so obtained is passed into the accumulating zone whence it is passed in its entirety into the primary stripping zone, or in part into the stripping zone and in part into the hot reaction products leaving the conversion zone.

In order that the invention may be more fully set forth and more fully understood reference is made to the drawings accompanying and forming a part of this specification and which illustrate the form and manner in which the invention may be practiced Figure 1 is a more or less diagrammatic elevational view of apparatus for carrying out the process in accordance with the invention.

Figures 2 and 3 are more or less diagrammatic views of apparatus suitable for carrying out, in a modied form, the operations eifected in the recovery phase of the process in accordance with the invention and in which parts of apparatus identical with those shown in Figure l are identied with like reference numbers.

The following illustrative description of the process in accordance with my invention is made with reference to Figure 1 of the attached drawings. A mixture of normally gaseous hydrocarbons from any suitable source is forced by means of pump 2 through lines I, 4 and 5, controlled by valves 3 and i, into a primary stripping zone. The primary stripping zone may consist of a suitable fractionating tower 1. By closing valve 6 the charge may be passed from line I into line 8 controlled by valve 3 and through cooler I 0 and line into fractionator 'I. Fractionator 'I is maintained at a relatively high pressure, for example, at about 350 to 450 pounds, preferably about 400 pounds. In fractionator 'I the normally gaseous hydrocarbon charge is separated into a lighter normally gaseous fraction and a accepte Vcarbon refrigerant entering the cooling zones.

normally gaseous fraction comprises hydrogen, methane, ethane, ethylene and some hydrocarbons having more than two carbon atoms to the molecule, for example, propane and propylene. 'I'he heavier normally gaseous hydrocarbon fraction comprises normally gaseous hydrocarbons having more than two carbon atoms to the molecule. This stripping action within fractionator l is aided by means of a reboiler i I equipped with a closed coil I2 through which a suitable heating medium is pasesd. Liquid in the lower part of fractionator lcirculates through line I3 into reboiler II and material vaporized therein returns to fractionator 'i through line I4.

The heavier normally gaseous hydrocarbon fraction, comprising hydrocarbons having more than two carbon atoms to the molecule separated in fractionator l, is drawn continuously from reboiler II and forced by means of pump l5 through lines l5, Il' and i8 at a high pressure in excess of 400 pounds, for example, about 1800 to 2200 pounds, into a thermal conversion zone. The thermal conversion zone may consist of an externally heated coil I9 suitably positioned in a furnace 20 provided with suitable heating means. The invention is not limited to the use of a conversion zone comprising only one coil, for example, two or more externally heated coils positioned in suitable radiating and convection sections of a furnace may be used, through which coils the normally gaseous hydrocarbons undergoing conversion are made to pass in parallel streams.

Indirect heat exchangers 2| and 22 are positioned in line I8. By passage through heat exchangers 2| and 22, the heavier normally gaseous hydrocarbon fraction, comprising hydrocarbons having more than two carbon atoms to the molecule, is preheated to a temperature in excess of 400 F., for example, about 600 F. to 700 F. Within conversion coil I9 the preheated normally gaseous hydrocarbon strean under high heavier normally gaseous fraction. The lighter pressure is raised to a high temperature of from 750 F. 1250 F., for example, about 950 F. to

1100 F. to effect the conversion of normally gaseous hydrocarbons into normally liquid products.

AHot reaction products, comprising polymerized normally liquid hydrocarbons, leave conversion coil I9 through line 23 leading to fractionator 25. By controlled manipulation of valves 26 and 21 a part of the' normally gaseous hydrocarbon stream owing under high pressure through line I6 may be passed through line 28 into line 23 to quench the hot reaction products leaving conversion coil I9. If desired, additional quenching medium, for example, gas oil, may be drawn from an outside source and forced through line 29 controlled by valve 30, and line 3| into line 23. Sumcient quenching medium is added to the hot reaction products leaving conversion coil I9 through line 23, to lower their temperature suiciently to arrest the progress of polymerization reactions, the temperature of the hot reaction products at this point in line 23 thereby being reduced to about 750 to 950 F., for example, 850 F.

The quenched reaction products flowing through line 23 are passed through indirect heat exchanger 22 interposed in line 23 whereby they are further cooled by indirect heat exchange with the normally gaseous hydrocarbon stream passing through line I8 to conversion coil I9. By manipulation of valves 32, 33 and 34 a part or all of the reaction products owing through line 23 through line 35 can line 23 may be drawn from line 23 after having passed through indirect heat exchanger 22 and caused to now through line 35. Line 35 passes through reboiler 38 wherein the reaction products are further cooled by indirect heat exchange with liquid drawn from the bottom of vfractionator 25, thus providing heat necessary to aid in thestripping operation in fractionator 25. After passing through reboiler 35 the partially cooled reaction products continue through line 35 and 10 reenter line 23 at a point beyond valve 32.

Although in the 'present illustrative example of the invention hot reaction products are used to reboil the material from but one .fractionator the process. in accordance with the invention is not to be limited to this extent. Thus a part or all of the hot reaction'products passed from be caused, if desired, to passl through additionalreboilers associated with other fractionating towers of the system before being returned to line 23.

By manipulation of valves 31, 33 and 39 reaction products iiowing through line 23 may, in part or in entirety, be diverted through line 4I! passing to indirect heat exchanger 2l wherein'25 they are subjected to indirect heat exchange with the normally gaseous hydrocarbon stream passing through line I8 to heat exchanger 22.. Reaction products leaving heat exchanger 2| continue through line 4I to reenter line 23 at a point 30 intermediate valve 31 and an expansion valve 42. By manipulation of valve I3 a part of the normally gaseous hydrocarbon stream flowing through line I'I may be passed through line M into line 23 at a point before expansion valve I2 35 to thereby further cool the reaction products prior to their passage through expansion valve 42.

The partially cooled reaction products in passing through valve 42 are reduced in pressure to, 40 for example, about 350 to 450 pounds, preferably about 420 pounds. The cooled reaction products after reduction in pressure continue through line 23, passing through cooler 45 where additional cooling may be eifected if desired, and 45 enter into fractionator 25.

By careful regulaton of valves 32, 33, 3l, 31,

38 and 39 the quantity of reaction products passed through either reboiler 3B or heat exchanger 2I, or both, may be controlled and the 50 hot reaction products thereby cooled to a desired temperature, for example 200 F. to 450 F. prior to their entering fractional-,or 25. This provides an extremely exible means for distributing in a well-balanced manner the available heat in the hot reaction products leaving conversion coil i9.

It is to be understood that this feature of the invention is not limited to the use of heat exchangers 22 and 2l as shown in the present illus- 50 trative description of the invention. Heat exchanger 2I may suitably be replaced by a plurality of'indirect heat exchangers through which the normally gaseous hydrocarbon stream passing through line I8 to conversion coil I3 may be 65 caused to flow in part or in its entirety, in parallel or in series. The hot reaction products emanating from conversion coil Icouldv thus be suitably. passed in its entirety or in part, in series or parallel through such a plurality of indirect heat exchangers to preheat the normally gaseous hydrocarbon charge ilowing through line i8 to conversion coil I9.

In accordance with the invention it is further intended that if desired the normally gaseous hydrocarbon stream flowing through line I8 to conversion coil I3 be divided into two separate streams passing through separate pluralities of indirect heat exchangers to separate conversion coils or separate pluralities of conversion coils.

The hot reaction products emanating from such separate conversion coils can thus be caused to ilow in dual ow through the separate pluralities of indirect heat exchangers to preheat the normally gaseous hydrocarbons flowing to the conversion coils.

Within fractionator 25, maintained at a pressure of, for` example, 350 to 450 pounds, preferably about 410 pounds, products emanating thereto through line 23 and comprising products resulting from conversion reactions effected within conversion coil I9 are separated into a normally gaseous fraction comprising hydrocarbons having four carbon vatoms to the molecule and less and hydrogen, and a normally liquid fraction comprising hydrocarbons having iive or more carbon atoms to the molecule. By means of line 50 liquid in the bottom of fractionator 25 is passed into reboller 36 wherein, by control of valves 32, 33 and 3l, sufiicient heat is absorbed from the hot reaction products passing through line 35 to eii'ectively aid in stripping of constituents having less than ve carbon atoms to the molecule from the normally liquid fraction separated from the reaction products in fractionator 25. Such stripped constituents are returned to .fractionator 25 through line 5I.

The normally gaseous fraction separated in fractionator 25 is passed from fractionator 25 through line 52 and cooler 53 into accumulator 54. In cooler 53 the hydrocarbon stream is cooled to a temperature, for example, not exceeding 210 F. resulting in the condensation of heavier constituents of the hydrocarbon stream, which condensed material, comprising, for example, hydrocarbons having four carbon atoms to the molecule, is separated from the remaining uncondensed stream in separator 5I and forced by means of pump 55 through line 56 and cooler 5T, as reflux, into the top of column 25.

Normally gaseous hydrocarbons areA passed from accumulator 54 through line 58 controlled by valve 59 and lines 60, cooler III and line 5 into fractionator 'I wherein they are separated, together with the fresh charge, into a lighter normally vgaseous hydrocarbon fraction and a heavier normally gaseous hydrocarbon fraction.

The normally liquid fraction, -separated in fractionator, 25, is continuously drawn from reboiler 35 and passed through line 6I and expansion valve 52 Vinto fractionator 63. In passing through expansion Vvalve 62 the stream iiowing through line 6I to fractionator .63 is substantially reduced in pressure so that it enters fractonator 53 at a pressure of, for example, not exceeding pounds. Within fractionator 53 constituents boiling above the motor fuel boiling range are separated as ay liquid fraction from lighter constituents comprising polymerized products boiling within the gasoline boiling rangel Heat required to effectively aid in the substantially complete stripping within fractionator 53 of the Vgasoline from the heavier constituents is provided by4 passage of liquid from the bottom -of fractionator 53 through line 6I, into reboiler 55. Reboiler 55 is equipped with a closed coil 51 .through which a suitable heating medium,

which may suitably be part of the hot reaction products nowing through line 35, is caused to iiow. Stripped gasoline constituents are returned to fractionator 63 through line 98.

Liquid comprising constituents boiling above the motor fuel boiling range is drawn continuously from fractionator 83 through line 64, reboiler 65, line 88 and line 69 controlled by valve I and eliminated from the system. If desired a part of the liquid so drawn from fractionator 53 through reboiler 85, may be forced by means of pump through line 16, controlled by valve 11, and line 3| into line 23 carrying the hot reaction products leaving conversion coil i9.

The gasoline fraction separated within fractionator 53, comprising lighter constituents which may have passed into fractionator 93, leaves the upper part of fractionator 83, through line 18 and passes through cooler 19, wherein normally liquid products arev condensed, into accumulator 89. Within accumulator 80 the condensed normally liquid products are separated from any remaining normally gaseous constituents. Liquid comprising desired constituents boiling within the motor fuel boiling range is drawn from accumulator 89 through line 8i controlled by valve 82 and eliminated from the system as a desired ilnal product. A part of the liquid separated in accumulator 80 is forced through line 83 by means of pump 84 as reux to the top of fractionator B3.

Normally gaseous constituents. for example, hydrocarbons having less than live carbon atoms .to the molecule, separated in accumulator 80 are forced by means of pump 85 through line 86, line 81 controlled by valve 88, and line 60, cooler I0 and line 5, into fractionator 1.

The lighter normally gaseous hydrocarbon fraction comprising hydrocarbons having less than three carbon atoms to the molecule and hydrogen, separated in fractionator 1 will comprise some quantity of hydrocarbons having more than two carbon atoms to the molecule as, for example, hydrocarbons having three carbon atoms to the molecule, which it is desired to include in the charge to the polymerization zone.

It is the purpose of the subsequent stage of the operation ofthe process in accordance with the linvention to eiIect the substantial recovery of hydrocarbons having more than two carbon atoms to the molecule from the lighter normally gaseous hydrocarbon fraction separated in fractionator 1. Accordingly the lighter normally gaseous hydrocarbon fraction is passed overhead from fractionator 1 through line 90 and cooler 9| into a carbons having three and less carbon atoms to the molecule and hydrogen leave separator 92 through line 96 at a temperature of, for example, not exceeding about 85 F., preferably about 60 F., and at a pressure of, for example, about 340 to 440 pounds, preferably about 400 pounds. The gaseous stream passing through line 95 enters dehydrators 96 and 96a which are arranged so that the gas may pass therethrough in series or in parallel by judicious manipulation of valves 91, 91a, in line 98 andvalves 99, 99a inline |00. For example, the gaseous stream may ow from line 95 through line 98, valve 91 into dehydrator 9B, valve 91a being closed. Dehydrators 96, 98a may be of any desired type and in the present illustration of the invention consist oi chambers charged with a suitable dehydrating agent such as, for example, alumina and silica gel. In dehydrator 98 water is removed 'from the gaseous stream to avoid subsequent freezing of constituents in the gaseous stream and diiiiculties resulting therefrom. From dehydrator 9B, the dehydrated gaseous stream passes through line |80, valve 99, valve 99a being closed, and line |0| into indirect heat exchanger 02.

In indirect heat exchanger |02 the gaseous stream is subjected to' indirect heat exchange with a refrigerating medium, for example, boiling propane, resulting in the cooling of the stream to, for example, 30 to 40 F., preferably to below 35 F., and eecting liqueiaction of hydrocarbons having more than two carbon atoms to the molecule. The cooled stream is passed from exchanger |02 through line |03 into a. separating zone which may suitably consist of a fractionfrom fractionator |04 through line |05 into a' second indirect heat exchanger |06 wherein the gaseous stream is further cooled to a temperature of, for example, 10 F., thus effecting liquefaction of remaining hydrocarbons having more than two carbon atoms to the molecule. The cooled stream is passed from exchanger |06 through line separator 92. Separator 92 may suitably consist of a column provided with bailies or trays.

In passing through cooler 9| the gaseous stream will be cooled to a temperature, for example, be-

low 130 F., and preferably about 100 F. thereby effecting condensation of heavier constituents in the gaseous stream comprising some hydrocarbons having three carbons to themolecule and any 'heavier constituents which may have passed over into line 90. In separator 92 further liquefactionof the heavier components of the normally gaseous hydrocarbon stream is brought about by the introduction into the top of 'separator 92 of cold recovered liquefied hydrocarbons having more than two carbon atoms to the molecule. Liqueed normally gaseous hydrocarbons are takenfrom the bottom of separator 92 and pumped through line 93 by means of pump 94 into the upper part of fractionator 1. The liquid so introduced into the top of fractionator 1 through line 93 functions as reflux for fractionator 1. I

Normally gaseous products comprising hydro- |01 into separator |08. From the bottom of separator |08 the liqueed constituents are forced through line |09 by means of pump ||'0 into the upper part of fractionator |04.

Liquid products comprising hydrocarbons having more than two carbon atoms to the molecule are drawn from the bottom of fractionator |04 and forced bymeans of pump through line |2 into the upper part of separator 92.

Gaseous products substantially free of hydrocarbons having more than two carbon atoms to the molecule and comprising hydrogen, methane, ethane and ethylene leave separator |08 through line ||5 at a temperature of, for example, 0 to 10 F. and a pressure of about 325 to 425 pounds, for example, about 385 pounds.

The low temperature and high pressure of the gaseous stream leaving separator |08 through the line ||5 is utilized to cool and compress at least a part of the refrigerant used as the cooling medium in indirect heat exchangers |02 and |06.

For this purpose the cold gaseous stream leaving separator |08 through line ||5 is passed operation,

panded stream leaving expansion side of compressor |'1 will, as a result of the expansion, have lowered its temperature to a temperature of, for example, -25 to 35 F. This low temperature of the expanded gaseous stream is utilized by passage through indirect heat exchangers H and wherein it serves to cool a part of the refrigerating medium destined to cool indirect heat exchangers |02 and |06. From exchanger |20 the expanded gaseous stream passes through line |2| controlled by valve |22 to be eliminated from the system.

A part-of the gaseous stream to be eliminated from the system through line |2| may be used to dry the dehydrating material in dehydrators 06, 96a after the latter has become charged with moisture removed from the hydrocarbon stream treated. By the proper manipulation of valves |22 and |23 a part or all of the gas passing from exchanger |20 through |2| ymay be diverted through line |24 to dehydrators 96, 06a. A heater |25 is interposed'in line |24 to heat the gas to a temperature suitable to the dehydrating for example, about 300 F. The heated |25 continues through line |24 and by the closing of valves |26, 01a, 03a, |21. and opening of valves |26a and |2141, is passed through dehydrator 36a to dehydrate the dehydrating material moisture removed from the dehydrating material flows out of dehydrator 66a through line |28 controlled by valve |2`|a and is eliminated from the system through line |20. Similarly by closing of valves |260., |26 and |21 the heated gas leaving heater |26 through line |24 may be caused to flow through gas leaving heater dehydrator 96, to dehydrate the dehydrating material .therein and be eliminated 'therefrom' through line |23 controlled by valve |21. It is thus possible to dehydrate one of the dehydrators 96, 95a while the other remains in operation.

A liquefied normally gaseous refrigerating medium for example, a liquefied normally gaseous hydrocarbon, is drawn from an accumulator |32. Although propane is a preferred refrigerant and is used in the present description of an illustrative example of the invention, the process according to the invention is not limited to to the use of this particular hydrocarbon as the refrigerating medium and other normally gaseous hydrocarbons or any other suitable refrigerating medium may suitably beused.

Accumulator |32 containing the liquefied pane refrigerant emanating from exchanger ||6 through line |38 is combined with the propane refrigerant vflowing* through line resulting in a combined stream having a temperature below through line |"and valve |46 into line |41 leading to the compressionl therein. 'Ihe gas containing 31, 93, |21a and opening of valves propane is maintained at a suitably high pressure,

for example, 185 to 250 pounds. From accumulator |32 liquefied propane is passed through line |33 controlled by exchanger |20 wherein it is subjected to indirect heat exchange with cold expanded gaseous products emanating from `the expansion side of compressor through line IIB, and indirect heat exchanger H0 to exchanger |20. In passing through exchanger |20 and into line |35 the temvalve |34 to indirect heat 'perature of the liquefied propane will be lowered to a temperature below 100 F., for example, about '70"y F. A further quantity of propane is I drawn fromv accumulator |32 through'line |36 controlled by valve |31 and passed into indirect heat exchanger ||6 wherein it is subjected -to-indirect heat exchange with cold normally gaseous products emanating'from separator |06 through line ||5. In passing through exchanger ||6 and into line |36 the temperature of the propane refrigerant will be reduced to a temperature below F., for example, about 20 F. The cooled proabout '70, for example, 45 F. iiowing through line |39 to propane drum |42. In passing through valve |40 in line |30 the liquefied cooled propane refrigerant isreduced to a pressure below 50 pounds, preferably 37 pounds, before entering drum |42, thereby insuring a liquid in the bottom of drum |42 at a temperature below 20 F., for example, 15 .11. From the bottom of drum |442 propane refrigerant is passed through line |43 into the cooling side of indirect heat exchanger |02 wherein the propane refrigerant is brought to its boiling point and vaporized by heat transferred to it from the hydrocarbon stream entering indirect heat exchanger |02 through line |0|. The vaporized propane refrigerantv is returned through line |44 from exchanger |02 to drum |42.

Vaporized propane leaves the top of drum |42 is passed in part through side of compressor ||1 wherein it is compressed to a pressure of about 200 to 250 pounds, for ex- -ample, about 230 pounds. The remainder ofthe vapor-ized propane refrigerant owing through 'line |45 is passed through line |43, controlled by valve |43, to compressor |50 wherein it is compressed -to a pressure of about 200 to 250 pounds, for example, about 230'pounds. l

Another stream of liquefied propane refrigerant is drawn from accumulator |32 and passed through line |5|, controlled by valve |62, into indirect heat exchanger 0 wherein its temperature is lowered to a temperature below 50 F., for example, 15 F., by indirect heat exchange with the expanded hydrocarbon stream manating from the expansion side of compressor |I1 through line IIB to exchanger ||9. From exchanger ||9 the cooled propane refrigerant is passed through line |53 and valve |54 into drum 55. In passing through valve |54 the propane refrigerant is reduced inpressure to a pressure below the maintained in drum |42, for example, 35 pounds, preferably'lO pounds, to assure liquid propane refrigerant-at the bottom of drum |55 at a temperaturebelow that of the liquid propane refrigerant within drum |42, for example, below 10 F.. preferably 20 F. From the bottom of drum |55 liquefied propane refrigerant is passed through line |56 to the cooling side of indirect heat exchanger |06. In cooling the hydrocarbon stream entering indirect heat exchanger |06 through line |05 the propane refrigerant is brought to the boiling lpoint and vaporized. The vaporized propane refrigerant is passed from exchanger |06 to drum |55 through line |51. Vaporized propane refrigerant is passed from the top of druml'l55 through line |58 to compressor |56v where it is compressed to a pressure of about 200 to 2 50 pounds, for exv valve |1|, into accumulator |12.

an outside source infn line |88 through line controlled by valve |88.

The process in accordance with the invention isin no wise limited to the temperatures and pressures of the propane refrigerant set forth herein as illustrative of the method of car. ying out the recovery phase of the process. The temperatures and pressures to be selected for the re-y frigerating medium are dependent upon the particular refrigerating medium used and the degree of recovery to be e'ected in the recovery phase of the process in accordance with the invention. It must be pointed out that the latent heat of vaporization of the propane refrigerant is relied upon to eil'ect a substantial part of the cooling in indirect heat exchangers |02 and |08.-

Valves |40 and |54 are therefore controlled to expand the cold, compressed, liqueed, propane refrigerant to a pressure which is slightly below the vapor pressure of boiling propane at the temperatures which are to be maintained in indirect heat exchangers |02 and |08.

A feature of the process in accordance with the invention is its adaptability to the processing of hydrocarbon mixtures in which the normally gaseous hydrocarbons which it is desired to subject to the conversion operation are in admixture with a substantial proportion of hydrocarbons heavier or lighter than those normally gaseous hydrocarbons which it is desired to subject to the conversion operation.

If, for example, a hydrocarbon mixture to be processed in accordance with the invention, from any suitable source, comprises normally gaseous hydrocarbons in admixture with an appreciable proportion of hydrocarbons having more than four carbon atoms to the molecule, it is charged to the system through line |10, controlled by Such charge may optionally be introduced simultaneously with separate introduction of normally gaseous hydrocarbons through line The pressure maintained in accumulator |12 will be governed by the type of operation carried out and may vary from. for example, about 300 pounds to a pressure substantially higher than that maintained in fractionator 1. Normally gaseous hydrocarbons may be drawn from accumulator |12 through line |13 and passed through lines 4 and 0 into fractionator 1, valves |14 and 8 being open. If desired the hydrocarbon stream may, by closing valve 8, be passed from line |13, through line 8 controlled by valve 9 and through cooler I0 and line 5 into fractionator 1.

When the hydrocarbons drawn from accumulator |12 through line |18, comprise hydrocarbons having more than four carbon atoms to the molecule it is preferred to force them by means of pump |15 through line |18 controlled by valve |11, and through line 28 controlled by valve 21 into line 22 carrying the hot conversion products emanating from conversion coil |9.

By control of valves 28 and 21 a part or all of the hydrocarbon stream flowing through line |18 may be passed from line- |10 through lines 28 and valve 28 into line I1 and combine therein with the normally gaseous hydrocarbon stream emanating from fractionator 1 through line |8 by means of pump I8.

If desired valve |18 may be opened to pass normally gaseous hydrocarbons from accumulator |12 through lines |19 and |80 into fractionator 1 while drawing liquids comprising normally gaseous hydrocarbons and some hydrocarbons having less than top of scrubber |84 trol of valves |18 carbons having more than four carbon atoms to the molecule from accumulator |12 through line |18.

If the hydrocarbons to be processed in the process in accordance with the invention consist ,of hydrocarbons comprising substantial amounts of normally gaseous hydrocarbons having less carbon atoms to the molecule than those desired to be subjected to the conversion operation they are introduced into the system through line |85.

When, for example. it is desired to process such a mixture the normally gaseous hydrocarbon mixture is drawn from an outside source and forced by means of pump |88 through line |85 into the lower part of scrubber |84 wherein the charge so introduced is scrubbed with a -suitable scrubbing medium, for example, gas oil, capable of absorbing hydrocarbons having more than two carbon atoms to the molecule which is introduced through line |81, controlled by valve |88, into the top of scrubber |84. Substantially all hydrothree carbon atoms to the molecule and hydrogen is passed from the through line |89 controlled by valve |90 and eliminated from the system.

Rich scrubbing medium, comprising absorbed normally gaseous hydrocarbons having more than three carbon atoms to the molecule, is taken from the bottom of scrubber |84 and forced by means of pump |99 through line |9|, provided with indirect heat exchanger |92, into stripping column |94. In stripping column |94 absorbed normally gaseous hydrocarbons are stripped from the absorbing medium. Heat necessary to the stripping operation is provided by means of reboiler |95 equipped with heating coil |88 through which a suitable heating medium is passed. Liquid from the bottom of stripping column |94 is circulated through line |91, reboiler |95 and the stripped constituents are returned through line |98. Lean scrubbing medium stripped of absorbed hydrocarbons is continuously taken from reboiler |95 and forced by means of pump |99 through line 200 into line |81 entering the top of scrubber |84. Lean scrubbing medium passing from reboiler |98 through line 200 passes through heat exchanger |92 wherein it is cooled by indirect heat exchange with the rich absorption medium flowing to stripping tower |94. A cooler 20| interposed in line 200 beyond exchanger |92 further cools the lean scrubbing medium to a temperature, for example, below 100 F. Normally gaseous hydrocarbons stripped from the rich scrubbing medium in stripping tower l |94 leave the top of stripping column |94 through line 202 controlled by valve 208 andpass into accumulator |12. A cooler 204 is interposed in line 202 to cool and condense hydrocarbons passing therethrough to accumulator |12. From accumulator |12 any uncondensed gases, which may comprise hydrocarbons having less than three carbon atoms to the molecule can, by conand 205 be passed either through line 208 to the bottom of scrubber |84 or through line |00 to the top of fractionator 1. A part of the liquid in accumulator |12 is drawn therefrom through line 281, controlled by valve 208 and sent by means of pump 209 as reflux to the top of stripping column |84.

When scrubber |84 is used in conjunction with the process in accordance with the invention. gases leaving'separator 80 and pumped through line 88 may, by closing valve 88 in line 81 and opening of valve 2|0 be passed into line |85 leading into lower part of scrubber |84.

primedinFlgureZand In accordance with the invention the charge to the system may consist solely oi a hydrocarbon mixture comprising substantial amounts or constituents lighter than those desired to be converted and which charge is introduced into the system as described through line |85. It is to be understood, however, that simultaneously with the charging of hydrocarbon mixtures comprising substantial amounts of hydrocarbons having l less than three carbon atoms to the molecule to bons having more than two carbon atoms to the molecule are recovered from the light normally gaseous hydrocarbon fraction separated in fractionator 1 is not limited in its application to the above illustrative example of carrying out the invention. Figures 2 and 3 of the drawings illustrate simpliiled forms of vappa 'tus suitable for carrying out this phase of the invention wherein parts of apparatus identical with those shown in Figure 1 are indicated by the same reference numerals, these reference numerals being double primed in Figure 3.

Referring to Figure 2, theL dehydrated normally gaseous hydrocarbon stream, comprising three and less carbon atoms to the molecule and hydrogen, emanating from dehydrators 96', Qi'a through line passes into indirect heat Aex changers |02. This stream is subjected to indirect heat exchange with boiling propane, resulting in the cooling of the normally gaseous stream to, for example, F. to 40 F., preferably below F., and eiecting liquefaction of hydrocarbon constituents having more than two carbon atoms to the molecule. The cooled and condensed normally gaseous hydrocarbons'are passed from indirect line |03' into fractionator |04. Within fractionator |04', separation of condensed hydrocarbons having more than two carbon atoms to the molecule from remaining gaseous components is effected and the remaining gaseous components comprising hydrocarbons having three or less carbon atoms to the molecule and hydrogen is passed from fractionator |04 through line |05 into a second indirect heat ,exchanger |06', wherein it is further for example, 10 F., of remaining hydrocarbons having more than two carbon atoms to the molecule.

The cooled stream is passed from indirect heat I exchanger |06' through line |01' into separatorv |08'. From the bottom oi separator |00' the liquefied gases are forced through line |09' by means of pump ||0 into the upper part of fractionator |04.

Liqueiied gases are drawn from the bottom of fractionator |04 and forced by means of pump through line I I2' into the upper part of separator 92 (Figure 1).

Gaseous products substantially free of hydrocarbons having more than two carbon atoms to the molecule and comprising hydrogen, methane, ethane and ethylene leave separator |08' through line 300 at a temperature of, for example, zero to 10 F. and a pressure of. for example, 325 to 425 pounds.

The low temperature of the gaseous stream leaving separator |08' through line 300 is utilized cooled to a temperature of.4

thus yeffecting liquefaction y medium,

to cool the refrigerant-.used as the cooling medium in exchangers |02 and |06'. To this purpose the cold gaseous stream leaving separator |08 vthrough line 300 is passed through indirect heat exchanger 30| wherein it is subjted to indirect heat exchange with the refrigerating thereby cooling the reirigeratlng medlum. The gaseous stream owing through line 300 leaves the system through line 302 controlled by valve 303. In a preferred method of operation the gaseous stream dowing through line 300 is reduced in pressure before entering exchanger 30| to thereby reduce the temperature of the heat exchanger |02' through stream before it enters indirect heat exchanger 30|- Liqueiied propane is drawn from a propane accumulator |32', maintained at a suitably high pressure of, for example. 185,v toV 250 pounds. From accumulator |32 the liquehed propane is passed through line 304, controlled by valve 305, to indirect heat exchanger 30| wherein it is .subjected to indirect neat exchange with me cold gaseous stream flowing through line 0. In passing through exchanger 30| the tempera ture of the liquefied propane will be lowered to a. temperature below F., for example, about 20 F. The cooled liqueiied propane is passed from exchanger 30| `through line I to drum III'. In passing valve 301 in line 3 the pres-I sure of the cooled liquened propane is reduced to a pressure below 50 pounds. for examplefS'Z pounds, thereby providing a liquid propane in drum |42' having a temperature below 20 F., for example,- 15 F. From the bottom oi' drum |42' liquid propane is drawn through line Ill and passed as cooling medium to exchanger |02 wherein the liquefied propane is brought to its boling point and vaporized by heat transferred to it from the gaseous stream entering indirect heat exchanger |02' through line III. The vaporized propane refrigerant is returned from exchanger |02' to drum |42' through line 100'.

A part of the liqueed propane drawn from drum |I2' through line 308 is passed through line 3|| and valve 3|2 into drum |55. In passing through valve 3| 2 the pressure on the liqueiied propane is reduced to a pressure of, for example, about 10 pounds to vprovide a liquid propane refrigerant in drum having a temperature of, for example, about 20 F. Liquid propane is drawn from the bottom'of drum |55' through line 3|3 and passed into indirect heat exchanger |00' as the cooling medium therefor.

Within indirect heat exchanger III the liquid propane refrigerant is brought to its boiling point and vaporized by heat extracted from the gaseous stream entering exchanger |00' through line |05. Vaporized propane refrigerant is returned grindrum |55'. from exchanger |06 through line Vaporized propane refrigerant is drawn from the top of drum |42 and passed through line lli to compressor 3H wherein'it is compressed to a 'pressure of about 185 to 250 pounds. Similarly vaporized propane refrigerant is drawn from the top of Adrum |55' and passed through line 3|8 to compressor 3|! wherein it is compressed to a pressure of about 185 to 2 50 pounds. Compressed propane refrigerant leaves compressor 3|1 through line 320 and compressor 3|! through line 32| into line 320. The combined stream of compressed propane refrigerant iiowing through line `320 passes through cooler 322 to propane refrigerant accumulating drum |32. In` cooler 3.22 the compressed propane refrigerant is cooled to a temperature of, for example, about 100 F. to liquefy it.

Additional propane refrigerant may be drawn from anoutside source through line 323 controlled by valve 324 discharging into line 305.

In the further modification of the recovery phase of the process in accordance with the invention as shown in Figure 3, the stream of normally gaseous hydrocarbons from which hydrocarbons having more than two carbon atoms to the molecule are to be separated, is passedconsecutively through the two refrigerating zones of the recovery phase oi the process without lseparation of any liquefied material from the stream between the two refrigerating zones.

The dehydrated normally gaseous hydrocarbon stream comprising hydrocarbons having three and less carbon vatoms to the molecule and hydrogen emanating from dehydrators 95", 96"a through line passes into indirect heat ex.- changer 350 wherein it-is subjected to indirect heat exchange with boiling propane. In indirect heat exchanger 350 the gaseous stream is cooled to, for example, 30 F. to 40 F., preferably below 35 F., resulting in liquefaction of hydrocarbons having more than two carbon atoms to the molecule. 'Ihe ,cooled gaseous stream passes from heat exchanger 350 directly intov indirect heat exchanger 35|. In indirect heat exchanger 35| the stream is further cooled to a temperature of, for example, F., thus effecting liqueflcation of remaining hydrocarbons having more than two carbon atoms.

The cooled stream is passed from exchanger 35| Y through line 352 into fractionator 353 wherein separation of liquefied normally gaseous hydrocarbons from uncondensed cooled gaseous products is effected. From the bottom of fractionator 353 the liquefied normally gaseous hy-b drocarbons having more than two carbon atoms to the molecule are withdrawn through line I2" and forced therethrough by means of pump'l to separator 92 (Figure 1).

Gaseous products substantially free of hydrocarbons having more than two carbon atoms to the molecule and comprising hydrogen, methane, ethane and ethylene leave the upper part of fractionator 353 through line 354 at a temperature of, for example, zero to -10 F. The low temperature of the gaseous stream leaving fractionator 353 through line 354 is made use of to cool the propane refrigerant used as the cooling medium in indirect heat exchangers 350 and 35|. To this purpose the gaseous stream owing through line 354 is passed through heat exchanger 355 wherein it is subjected to indirect heat exchange with the propane refrigerating medium. .After passing through heat exchanger 355 the normally gaseous stream is eliminated from the system through line 355, controlled by valve 351. If desired, the gaseous stream owing through line 354 may be reduced in pressure prior to its entry into heat exchanger 355 to thereby further lower its temperature prior to its entry into heat exchanger 355.

Liqueed propane refrigerating medium is drawn from accumulator drum |32" maintained at a suitably high pressure, for example, 185 to 250 pounds and passed through line 350 controlled by valve 36| to indirect heat exchanger 70 355. Within indirect heat exchanger 355 the propane refrigerant is cooled to a temperature Vbelow about 50 F., for example, about 20 F.

The cooled liquefied propane refrigerant is passed from indirect heatA exchanger 355 through line ecus stream entering ,propane refrigerant is reduced to a pressure below 50 pounds, for example, about 31 pounds. thereby providing a liquid propane in drum |42". having a temperature below 20 F., for example,

From the bottom of drum |42" liquid propane refrigerant is passed through line 355 into indirect heat exchanger 350 as cooling medium. In indirect heat exchanger 350 the propane refrigerant is raised to its boiling point and vaporized by heat withdrawn from the normally gasindireot heat exchanger- 350 through line lll-I". The Vaporized propane refrigerant is drawn from heat exchanger 353 and passed through linem351 to propane drum Similarly, liquid propane refrigerant is withdrawn from the bottom of propane drum |55" and passed through line 355v into indirect heat exchanger 35| aslcooling medium. Within indirect heat exchanger 35| Ythe propane refrigerant is raised to' the boiling point and Vaporized by heat withdrawn'from the normally gaseous stream passed to lindirect heat exchanger 35| from indirect heat exchanger 350. Vaporized propane refrigerant is drawn from indirect heat exchanger 35| and passed through line Y363 to propane drum |55".

Vaporized propane refrigerant is drawn from `the top of propane drum |42 and passed through line 310 to compressor 31| wherein it is compressed to a pressure of, for example, 185 pounds to1250 pounds. The compressed propane refrigerant leaves compressor 31| through line 312. Similarly, Vaporized propane refrigerant is withdrawn from propane drum |55" and passed through line 313 to compressor 314 wherein it is compressed to a pressure of, for example, 185 to 250 pounds. The compressed propane refrigerant leaves compressor 314 l'through line 315. Compressed propane refrigerant flowing through lines 312 and 315 is combined into a single stream flowing through line 315 to propane accumulator drum |32. Line 315 is provided with a, cooler 311 wherein the compressed propane refrigerantis cooled to a temperature below 120 F., for example, F. to liquefy it.

Additional propane refrigerant may be added to the system from an outside source through line 318, controlled by valve 313, discharging into line 310.

While the recovery systems shown in the drawings are especially adapted for removing desired hydrocarbon constituents from gases and vapors passing overhead from separator 92, the recovery systems may be used for separating desired hydrocarbons, such as C: and C4 hydrocarbons, from gaseous mixtures containing hydrocarbons and derived from other For example. gaseous mixtures containing Y higher and lower molecular weight hydrocarbons, such as, crackirm still gases or. natural gas may be introduced into any oneof lines 95, 35' and 35" and passed through either one of the dehydrators 35 or 35a,

96' or s'a or 96?' or "a to dry the gaseous mixture ahd the dried gaseous mixture is then passed through the rest of the'recovery system to cool and liquefy higher moleculark weight hydrocarbons. The liquefied hydrocarbons are separated from unliquefied gases andare passed through line H2 or line III' or line H2", associated, respectively, with dehydrators -"a, 96'98a or 96-96"a, and may be withdrawn from the system and further treated as desired or they may be passed to the separator 82. Where natural gasoline is recovered from natural gas, it is preferably withdrawn from the system.

While the invention has been described hereinabove with respect to specific examples of the mode of operation, it will be understood by those skilled in the art that the invention is not limited'to such illustrative examples but may variously be practiced and embodied within the scope of the claims hereinafter made.

We claim: i

1. A process for separating heavier .normally gaseous hydrocarbons y:from a mixture of normally gaseous hydrocarbons wherein normally gaseous hydrocarbons are charged to a fractionating zone,- separating said normally gaseous hydrocarbons in said fractionating zone into a fraction comprising lighter normally gaseous hydrocarbons and a fraction comprising heavier normally gaseous hydrocarbons, passing said. fraction comprising lighter normally gaseous hydrocarbons through a drying zone, passing said dried fraction through a cooling zone wherein it is indiv rectly contacted with a liqueed refrigerant under high pressure to cool said fraction and condense additional heavier normally gaseous hydrocarbons therefrom, passing said cooled fraction through a second cooling zone wherein it is indirectly contacted with a liquefied refrigerant under lower pressure than said refrigerant bons to said fractionating zone, withdrawing vaporized refrigerant from said cooling zones,

expanding said cooled uncondensed normally gaseous hydrocarbons, utilizing the energy made available by said expansion to compress at least a part of said vaporized refrigerant, to a high pressure, cooling said compressed refrigerant to' liquefy it, passing said liquefied refrigerant to a common source of supply, withdrawing a portion of liquefied refrigerant from said common source of supply, cooling said portion of liqueed refrigerant by indirect contact with said cooled uncondensed normally gaseous hydrocarbons prior to said expansion step, withdrawing a second portion of liquefied refrigerant from said common source of supply, cooling said second portion of liquefied refrigerant by indirect contact with said expanded normally gaseous hydrocarbons and using said cooled portions of liqueed refrigerant as the refrigerant in said cooling zones.

2. Process in accordance with claim 1 wherein said cooled refrigerant compressed to high pressure is reduced in pressure before entering said cooling zones to a reduced pressure which will maintain said refrigerant entering said cooling zones in a liqueed state and permit vaporization of said liquefied refrigerant during the cooling process in said cooling zones. Y

3. A process in accordance with claim 1 wherein llquifled propane is used as said refrigerant.

PERC'IVAL c. KEITH, Jn. LUTHER n. mur 

